The intrinsic myenteric innervation of the hind-gut and accessory muscles of defaecation in the cat

Age-related changes in substance P-immunoreactive nerve structures of the rat recto-anal region

The recto-anal region is innervated by extrinsic and intrinsic nerves and a number of neuropeptides including substance P (SP) have been suggested to participate in the regulation of intestinal movements. We examined the age-related changes in the distribution of SP-immunoreactive nerve structures in the distal part of the rat large intestine. Using immunohistochemistry, the presence of SP was studied in fresh tissues from Wistar rats at different ages taken at three sampling sites, the distal rectum, anal canal and internal anal sphincter. In the 15-day old rats the myenteric plexus of the distal rectum and anal canal was well outlined by numerous SP-immunoreactive varicose nerve fibres encircling immunonegative perikarya. In the circular muscle layer, nerve fibres and small nerve bundles ran parallel to the muscle cells, while in the longitudinal muscle layer, only occasional nerve fibres were seen. At the level of the internal anal sphincter, no myenteric ganglia were present. Here, thin varicose fibers ran parallel to the smooth muscle cells. In the 3-month old rats, a larger number of intensely staining SP-immunoreactive nerve fibres were found and in the circular muscle layer, thicker nerve strands were observed. In the 26-month old rats, the density and staining intensity of SP-immunopositive nerve fibres in the myenteric plexus was lower than in the 3-month-old rats. Similar changes in the SP-immunostained fibres in the internal anal sphincter were observed. Degenerative alterations in SP-containing fibres during aging appear to play a role in ano-rectal motility and sphincter control.

Myenteric plexus of the hind-gut: developmental abnormalities in humans and experimental studies

Intraluminal pressure studies on patients with congenital aganglionosis showed that the aganglionic rectum contracted in an uncoordinated manner and failed to relax. Histochemical assessment of the innervation helped to explain the variable severity of the symptoms in this condition. It is concluded that (1) absence of ganglia prevents normal coordinated peristalsis and creates an obstructive element; (2) absence of reflex relaxation adds to the obstruction; (3) the degree of uncoordinated motor activity in distal aganglionic bowel probably relates to the number of cholinesterase-positive nerves in the circular muscle and adds another variable obstructive element; and (4) deficient innervation of distal ganglionic bowel probably creates a poor propulsive force and so accentuates more distal obstructive factors. Neurohistochemical and functional studies in the anorectum of cats reveal a somewhat different innervation pattern from that in humans but show that sphincteric tone is mainly due to alpha-adrenergic neural activity. Reflex relaxation of the internal anal sphincter is a complex function in which inhibitory responses override motor responses, and it involves an important non-adrenergic non-cholinergic component. The role of cholinergic nerves in the sphincter remains uncertain. Neurohistochemical assessment of full thickness biopsy specimens of rectal muscle from patients with disabling constipation shows that developmental neuronal dysplasias of the hind-gut may be divided into three main categories: (1) aganglionosis (Hirschsprung's disease), (2) hypoganglionosis and (3) hyperganglionosis, and that the different neuronal elements may be affected to differing degrees in individuals within each group. Resection of the aganglionic bowel is required in congenital aganglionosis but the combined diagnostic-therapeutic procedure of anorectal myotomy has been found beneficial in patients with hypoganglionosis.

Discharge patterns of intramural mechanoreceptive afferents during selective distension of the cat's rectum

The afferent input from the rectum to the central nervous system (CNS) has yet to be thoroughly characterized. The characteristics of mechanoreceptive rectal afferents have been studied in unanaesthetized decerebrate cats. Following lumbo-sacral laminectomy, single-unit activity (occasionally multi-unit activity) was recorded from centrally cut filaments of the sacral dorsal roots (predominantly S2), while a balloon was inflated in the rectum. Starting from their background activities (mean 15.1 imp sec-1, SD 7.6 imp sec-1), afferent discharge rate increased with increasing balloon pressure (mean threshold 6.3 mmHg, SD 3.6 mmHg). The dependence of firing rate on intrarectal pressure began to flatten out at 25 mmHg (mean; SD 10 mmHg). For 22 out of 29 units (76%) complete saturation occurred at 35 mmHg (mean; SD 15 mmHg) with a maximum discharge rate of 31 imp sec-1 (mean; SD 12.6 imp sec-1). In a number of recording sessions, cyclical rectal contractions were observed. In these cases, changes in firing of the units were closely related to changes in intrarectal pressure. Pressure-related afferent activity could be enhanced by parasympathomimetic drugs which augmented rectal contractions. We conclude that sacral dorsal roots contain afferents from low-threshold mechanoreceptors located in the rectal wall, and that these afferents monitor the filling state and contraction level of the rectum.

The role of nitric oxide in the acetylcholine-induced relaxation of the feline internal anal sphincter, in vitro

BACKGROUND

The relaxatory effect of acetylcholine was investigated on the feline internal anal sphincter (IAS), in vitro.

RESULTS

Acetylcholine (10, 30, 100, and 1000 microM) caused a concentration-dependent relaxation of the same magnitude in strips from the proximal and distal IAS. The antagonist of nitric oxide synthase, N omega-nitro-L-arginine (L-NNA; 1, 10, and 100 microM), in a concentration-dependent and stereospecific manner, blocked the acetylcholine-induced relaxation, leaving a residual response of 10-30%. The blocking effect of L-NNA (100 microM) could not be shown in tissues that had been incubated with the substrate for nitric oxide synthase, L-arginine (1 mM).

CONCLUSIONS

The present results suggest that the acetylcholine-induced relaxation of the IAS to a major extent is due to an activation of nitrergic, inhibitory motor neurons to the IAS.

Reflex interaction from the urinary bladder and the rectum on anal motility in the cat

The intrinsic recto-anal inhibitory reflex (RAIR) and the extrinsic vesico-anal excitatory reflex were studied in anaesthetized cats in order to explore the nervous components of anal pressure regulation. The magnitude of the RAIR was documented at varying levels of anal pressure. Minimal anal pressure during RAIR was positively correlated to anal pressure immediately prior to rectal distension. It was possible to elicit the vesico-anal excitatory reflex concomitantly with an ongoing RAIR. It was also possible to elicit a RAIR during the vesico-anal excitatory reflex. The magnitude of the pressor reflex response was not changed by concomitant activation of the inhibitory reflex and vice versa. This suggests an independent action on the internal anal sphincter (IAS) of the two reflexes. Spontaneous detrusor contractions were abolished by rectal distension. However, an escape phenomenon from this inhibition was observed, suggesting a spinal, associative, connection. The results support the concept of a direct action of both extrinsic and intrinsic nervous mechanisms on the smooth muscle of the IAS.

Histochemical study of the lumbar colonic nerve supply to the internal anal sphincter and its physiological role in dogs

The sympathetic innervation of the internal and sphincter (IAS) and its physiological role in maintaining sphincter tone were histochemically and mechanically studied in dogs anesthetized with pentobarbital sodium. Numerous catecholamine-fluorescent nerve fibers with varicosities were identified in the IAS of normal dogs. Such fibers were markedly reduced at one week and one month after resection of the hypogastric nerves (HGNs) or the lumbar colonic nerve (LCN), and disappeared after combined HGN and LCN resection. IAS tone decreased to 37.2% of baseline at 1 h after LCN resection and to 69.9% after HGN resection. It returned to the preoperative level at one week and one month after resection. The restored IAS tone was decreased again by acute transection of the previously intact HGNs or LCN. Combined LCN and HGN resection also caused a marked reduction of IAS tone (36.9%) at 1 h after the procedure, and was then restored to the preoperative level with time. The restored tone was not decreased by phentolamine administration. These findings confirmed that both the LCN and the HGN innervate the IAS and play a physiological role in the development of resting tone. The restoration of IAS tone after denervation may be due to intrinsic myogenic properties of the sphincter.

Enkephalins in the inferior mesenteric ganglion of the cat and in the area of the lower digestive tract innervated by this ganglion: quantification by radio-immunoassay and characterization by high pressure liquid chromatography

Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg-Gly-Leu were quantified and characterized in the cat inferior mesenteric ganglion and in the area of the lower digestive tract innervated by this ganglion, including the proximal colon, distal colon and internal anal sphincter. In the structures studied, the concentrations of enkephalins expressed as femtomole/mg of wet tissue ranged from 66 to 160 with Met-enkephalin, from 15 to 45 with Leu-enkephalin and from 2 to 12 for Met-enkephalin-arg-gly-leu. In the lower digestive tract, the Met- and Leu-enkephalin content decreased from the proximal colon to the internal anal sphincter. The Met-enkephalin versus Leu-enkephalin ratio of the structures investigated were as follows: inferior mesenteric ganglion 3.2, proximal colon 4.4, distal colon 5, internal and sphincter 4.5. In individual samples of all the structures assayed the results of high pressure liquid chromatography (HPLC) analysis pointed to the presence of authentic Met- and Leu-enkephalin. HPLC analysis could not be carried out on Met-enkephalin-Arg-Gly-Leu due to the very low concentrations of this peptide in all the structures assayed. Our results, combined with those of previous immunohistochemical and physiological studies, support the idea that enkephalins are involved in the nervous control of the motility of the lower digestive tract.

Actions of morphine and enkephalins on the internal anal sphincter of the cat: relevance for the physiological role of opiates

The effects of Leu-enkephalin, Met-enkephalin and morphine on the electrical activity of the internal anal sphincter were studied in anesthetized spinalized cats and in vitro on sphincteric muscle strips. All the effects of enkephalins and morphine were antagonized by naloxone (2 mg/kg, i.v. in vivo and 10(-6)M in vitro). In vivo, the enkephalins (0.01 mg/kg i.v.) and morphine (2 mg/kg, i.v.) decreased the amplitude of the excitatory responses evoked in the sphincter by stimulation of the hypogastric nerves. Opiates presumably act on the sympathetic nerve endings by reducing the release of noradrenaline. In vitro, the enkephalins (10(-6)M) and morphine (10(-6)M) had a similar inhibitory effect, indicating that opiates act, at least partly, at intramural level. In vivo, the enkephalins and morphine produced an inhibition of the spontaneous electrical activity of the internal anal sphincter. This inhibition occurs also in vitro; it is thus due to a peripheral effect of opiates acting either directly on the sphincteric smooth muscle cells, or through the nervous structures controlling sphincteric motility. In addition, the distribution of nerves containing enkephalin-like immunoreactivity, using whole mount preparations of cat internal anal sphincter, indicates that this area is supplied with a dense Leu- and Met-enkephalinergic innervation. Met- and Leu-enkephalin-like immunoreactive axons were detected within the circular and longitudinal muscles.

Studies on the integrated extrinsic nervous control of rectal motility in the cat

The effect of sympathetic nervous activity on rectal motility induced by pelvic nerve stimulation (PNS) was studied in anaesthetized cats. Division of the sympathetic lumbar colonic and hypogastric nerves or alpha-adrenoreceptor blockade, both of which reduced rectal tone, also reversed a predominantly relaxatory pelvic nerve response into a pure contraction. Contractions to pelvic nerve stimulation were reduced by simultaneous lumbar colonic nerve stimulation. This lumbar colonic nerve-induced inhibition was augmented by alpha-adrenoceptor blockade and abolished by beta-blockade. Close intra-arterial injection of a beta-adrenergic agonist reduced contractions to PNS, while an alpha-adrenergic agonist had no effect. Stimulation of the hypogastric nerves enhanced rectal contractions to simultaneous PNS. The apparent similarity with the arrangement of extrinsic nervous control of the internal anal sphincter suggests that the rectum is functionally involved in continence mechanisms.

Three serial neurones in the innervation of the colon by the sacral parasympathetic nerve of the dog

Electrophysiological and histological techniques were used to study the nature of the innervation of the colon by the sacral parasympathetic nerve of the dog. Many cells which incorporate horseradish peroxidase (HRP) were observed in ganglia of the pelvic plexus, but not in the sacral cord, after HRP was injected into the wall of the distal colon. Stimulation of the pelvic ganglia by an application of dimethylphenylpiperazinium contracted the distal colon. The contraction was reduced by nicotine applied to the colon. Compound action potentials in responses of rectal strands of the pelvic nerve to stimulation of the sacral ventral roots decreased or disappeared after hexamethonium bromide (C6) was applied to the pelvic plexus. Conduction velocities of the potentials showed that most of the preganglionic fibres were B fibres, and nearly all the post-ganglionic fibres were C fibres. Many C fibres were observed by electron microscopy in the rectal strands after degeneration of the pelvic and hypogastric nerves. Stimulation of such rectal strands caused a contraction of the colon, which diminished after C6 was applied to the distal colon. These results show that the sacral parasympathetic nerve innervating the colon comprises three serial neurones located in the sacral spinal cord, the pelvic plexus and the myenteric plexus.

Efferent sympathetic nervous control of rectal motility in the cat

The sympathetic nervous control of rectal motility was studied in anesthetized cats. Division of the sympathetic nerves, i.e. the hypogastric nerves and the lumbar colonic nerves and alpha-adrenergic blockade reduced rectal tone indicating that these nerves are tonically active. Efferent electrical stimulation of the nerves at high intensities caused an immediate and sustained contraction which was inhibited after phentolamine but unaffected by hexamethonium suggesting a direct alpha-adrenergic effect on the rectal smooth muscle. However when prevailing rectal tone was high beta-adrenergic inhibitory responses unaffected by hexamethonium were observed. In addition the hypogastric nerves seem to convey cholinergic excitatory fibres to the rectum. The results imply that the sympathetic nerves are integrated in the nervous regulation of rectal motility in a fashion similar to the nervous control of the internal anal sphincter.

Nervous control of the internal anal sphincter of the cat

1. The effects of sympathetic and parasympathetic efferent nerve stimulation on the activity of longitudinal and circular coats of th anal sphincteric area have been studied on acute animals using extracellular electrical recordings. In addition, the effect of intramural sympathetic nerves stimulation has been investigated on anal sphincteric circular muscle, with the sucrose gap technique. 2. Hypogastric nerve stimulation elicited in anal sphincteric circular muscle slow time course depolarization responses (latency 200-400 msec) which were abolished by alpha-adrenergic blockers (dihydroergotamine, phentolamine). 3. Stimulation of the parasympathetic outflow to the internal anal sphincter (second ventral sacral root: VS2) inhibited spontaneous electrical activity of the circular muscle. Pharmacological arguments lead to the conclusion that the inhibition induced by VS2 stimulation is mediated through intramural non-adrenergic non-cholinergic (purinergic) inhibitory neurones. 4. Rectal distension caused an inhibition of the anal sphincteric circular muscle activity which persisted in the presence of atropine, phentolamine and propranolol, indicating that this inhibition was produced by non-adrenergic non-cholinergic intramural neurones. 5. VS2 stimulation produced only an activation of the longitudinal muscle of the sphincteric area, which was abolished by hexamethonium and atropine; in contrast, hypogastric nerve stimulation gave rise to an inhibition which was blocked by propranolol. These results indicate that the longitudinal muscle receives (1) an excitatory innervation from preganglionic parasympathetic nerves connected with intramural cholinergic neurones, and (2) an inhibitory sympathetic innervation from noradrenergic axons running in the hypogastric nerves. No inhibitory no-adrenergic non-cholinergic innervation was observed in the longitudinal muscle in response to VS2 stimulation. 6. The results obtained from simultaneous stimulation of VS2 and hypogastric nerves indicate that in the anal sphincteric circular muscle the release of noradrenaline from sympathetic nerves is modulated by cholinergic receptors located on noradrenergic nerve endings, muscarinic receptors which can abolish the release of noradrenaline, and probably nicotinic receptors which increase the noradrenaline release. The eventual functional significance of the nicotinic receptors is discussed.

A non-adrenergic nerve ending containing small granular vesicles in the guinea-pig gut

Two distinct types of small granular vesicle(SGV)-containing nerve ending are described in the gastrointestinal tract of the guinea-pig. One of these types of ending accumulates 5- and 6-hydroxydopamine (OHDA) and is therefore adrenergic. The other type remains unchanged after in vivo exposure to these drugs. The widespread distribution of this nerve in the smooth muscle layers of the large and small bowel suggests that it may play a role in gut motility.

Non-adrenergic, non-cholinergic (purinergic?) inhibitory innervation of the rabbit rectococcygeus muscle

A powerful non-adrenergic, non-cholinergic inhibitory innervation of the rabbit rectococcygeus was unmasked by atropine in preparations in which tone had been raised either by carbachol or prostaglandin E2-Flourescent histochemical localization of quinacrine (which binds ATP) revealed ganglia and associated nerve bundles which were neither adrenergic nor cholinergic both on the surface and within the rectococcygeus muscle. Treatment of the rabbit with 6-hydroxydopamine abolished catecholamine fluorescence without affecting quinacrine-stained neural elements. Release of ATP from the rectococcygeus increased 2-4 times above background levels during stimulation of intramural inhibitory nerves. In preparations in which the tone was raised, ATP caused an inhibitory response comparable to that produced by non-adrenergic, non-cholinergic nerve stimulation. Indomethacin reduced the increase in tone and spontaneous activity following washout of ATP in low tone preparations, and potentiated the relaxations produced by ATP in high tone preparations. These results suggest that the rabbit rectococcygeus, as well as receiving a cholinergic excitatory innervation and an adrenergic inhibitory innervation, is also innervated by purinergic inhibitory nerves.

Innervation of the rabbit rectococcygeus muscle and the functional relationship of the muscle to the terminal large intestine

1. The rectococcygeus muscle is supplied by cholinergic motor fibres from the parasympathetic division of the autonomic nervous system. 2. The histofluorescence technique reveals a sparse adrenergic innervation. 3. When a maintained state of partial contraction is induced by carbachol, stimulation of the extrinsic sympathetic nerves produces a relaxation of the muscle which is usually followed by contraction. 4. The rectococcygeus muscle may also receive nerves which are neither adrenergic nor cholinergic. 5. Ganglion cells have been found close to and, in some preparations, within the muscle; the role of these ganglion cells is not clear. 6. It would appear that the rectococcygeus muscle and the longitudinal muscle of the rectum are not linked by a myogenic mechanism. The rectococcygeus muscle would, however, appear to be linked by nerve fibres to neighbouring structures.

The inhibitory response of the rabbit anococcygeus muscle

1. Strips of rabbit anococcygeus muscle were submaximally contracted by the addition of phenylephrine to the bath fluid. 2. Acetylcholine, dimethylphenylpiperazinium and electrical field stimulation caused relaxation. Relaxation induced by acetylcholine and field stimulation was blocked by tetrodotoxin but only the acetylcholine-induced response was inhibited by lignocaine, tetraethylammonium and hexamethonium. The responses to both acetylcholine and field stimulation were resistant to atropine, practolol, and sotalol. 3. Relatively high concentrations of ATP caused relaxation. 4. Histological investigation did not show any cells resembling autonomic ganglion cells. 5. It is suggested that both acetylcholine and field stimulation release an inhibitory transmitter from nerve endings and that the release by acetylcholine is mediated through nicotinic receptor stimulation.

The internal anal sphincter in the cat: a study of nervous mechanisms affecting tone and reflex activity

1. Smooth muscle activities in rectum and internal anal sphincter have been recorded using intraluminal balloons.2. Reflex activation of the sphincter, caused by distension of the rectum, has been assessed before and after various combinations of blocking drugs.3. Responses to stimulation of hypogastric or sacral nerves, or to the administration of drugs with autonomic actions have been tested before and after various combinations of blocking drugs.4. Results indicate that the tone of the internal anal sphincter is influenced by a number of neural mechanisms. These include motor pathways involving both alpha-adrenergic and cholinergic mechanisms and inhibitory pathways involving both beta-adrenergic and non-adrenergic non-cholinergic mechanisms.5. Cholinergic contractions of the sphincter were converted to relaxations after alpha-adrenergic blockade. This indicates that the contractions are an indirect effect operating through an adrenergic reflex. Cholinergic relaxations may also be indirect and operate through reflex inhibition secondary to rectal contractions.6. Sphincteric motor activity is controlled largely through alpha-adrenergic mechanisms by adrenergic nerves acting directly on the muscle. beta-Adrenergic inhibitory mechanisms are thought to operate indirectly via ganglia.7. The over-all control of the sphincter is by complex reflex mechanisms involving numerous pathways and the activity of the sphincter at any one time is determined by the net balance between motor and inhibitory influences.8. Sacral nerve stimulation indicated that it contains cholinergic nerves to the rectum, non-adrenergic non-cholinergic inhibitory axons to the sphincter and variable numbers of adrenergic axons to the sphincter.9. Responses of the sphincter to drugs and nerve stimulation were often variable, as has been described many times in the literature. It is considered that this is due to complex combinations of indirect reflex effects, secondary to activation of structures outside the sphincter, operating with or against direct effects on the sphincter itself.